Cycling, self checking pressure sensing system

ABSTRACT

Cycling, self checking parameter sensing systems that continuously cycle such that the user of the monitoring system can determine not only if the vessel being monitored is above or below the desired parameter value, but also whether or not the monitoring system is functional. When the parameter being monitored is pressure, a system pressure chamber is attached to the vessel being monitored, and the pressure in this chamber is cycled to constantly test the function of the system components. The cycle is monitored for any irregularities.

This application claims the benefit of U.S. Provisional Application Ser.No. 60/056,781 filed Aug. 25, 1997.

BACKGROUND OF THE INVENTION

This invention relates in general to systems that monitor parameters inindustrial processes for parameter values that are outside of thedesired norm, and in particular to systems that monitor pressure vesselsfor over pressure or under pressure situations, and to equipment that isto be used in connection with devices that automatically shut down aprocess when an over pressure or under pressure situation could threatento rupture or collapse the pressure vessel.

Industrial operations, particularly those that include pressuresensitive operations, often require devices that monitor pressurevessels for over pressure or under pressure situations. These monitorsare connected to devices which may automatically shut down theindustrial process in an over or under pressure situation. One of theproblems with these systems is the inability to know if the monitoringsystem is actually functioning. For example, process materials may cloga sensing port, or otherwise prevent the pressure sensing device fromproperly monitoring system pressure. In instances where the monitoringsystem is relied upon to cause the emergency shut down of the process,it is critical that the system either function with 100% reliability, orthat the system somehow alert the operator of the facility that it isnot working properly, so that it call be repaired. Engineers haveimproved the reliability of critical shutdown system components in orderto improve the level of safety of a production process. However, whilethe reliability of monitoring systems has improved, they still are not100% reliable. Furthermore, it would be foolish to assume that a givensystem is 100% reliable, given the dangerous consequences of vesselfailure in an industrial process. Accordingly, it is most important toknow when a monitoring system has failed.

SUMMARY OF THE INVENTION

The instant invention provides a method and apparatus for monitoringprocess parameters in a manner that also informs the operator of thestatus of the monitoring system. Failure of the monitoring system isreadily identified, allowing for repair or replacement of the monitoringsystem, limiting the risk of an un-monitored out of norm parametervalue.

The instant invention creates a cycle that is monitored forirregularities in that cycle. A parameter sensing device is connected toa system to be monitored for the value of that parameter. The sensingdevice is then subjected to an artificially induced value of theparameter being monitored, such that a parameter value set point isreached. The reaching of this set point then triggers the cessation ofthe artificially induced value of the parameter. The parameter sensingdevice then returns to its initial state--that of monitoring the valueof the parameter in the system to be monitored. However, since theparameter set point is no longer being reached (assuming the value ofthe parameter in the system being monitored has not reached the setpoint) this in turn triggers the artificial induction of the value ofthe parameter. Accordingly, a cycle is created, wherein the parametervalue measured by the sensing device reaches the set point of thesensing device, and then returns to a value not reaching the set point.The cycle is disrupted if the equipment that creates the cyclemalfunctions in any way, or if the parameter value in the system beingmonitored has reached the set point. In this manner the invention notonly monitors the parameter in the system being monitored, but alsocontinuously checks to insure that the monitoring equipment isfunctioning properly. Disruptions in the cycle are recognized by adevice, such as a computer, that monitors the cycle, and alerts theoperator of the system to a potential problem.

A parameter that is often monitored is pressure in pressure vessels. Insuch an instance the instant invention may utilize a system chamber thatis attached to the vessel to be monitored. The pressure in the systemchamber is periodically raised using an independent gas source, until ahigh pressure switch attached to the system chamber is triggered (in anover pressure monitoring situation). This switch then triggers theopening of a solenoid valve, which in turn allows the gas in the systemchamber to be released into the vessel being monitored, lowering thepressure in the system chamber. The system chamber may be any convenientsize, and may be incorporated into the valve mechanism that connects theinstant invention to the vessel to be monitored. When the pressure inthe system chamber reaches a level below the set point of the highpressure switch, the solenoid valve is caused to close, which starts thecycle over again.

This pressure cycle in the system chamber is monitored. Changes in thecycle inform the operator of a problem with the monitoring system, or ofan over pressure or under pressure situation in the pressure vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will be made to the drawings wherein like parts are designatedby like numerals and wherein:

FIG. 1 is a plan view of a high pressure monitoring system of theinstant invention;

FIG. 2 is a plan view of another embodiment of a high pressuremonitoring system of the instant invention;

FIG. 3 is a plan view of another embodiment of a high pressuremonitoring system of the instant invention;

FIG. 4 is a plan view of another embodiment of a high pressuremonitoring system of the instant invention;

FIG. 5 is a plan view of another embodiment of a high pressuremonitoring system of the instant invention;

FIG. 6 is a plan view of a low pressure monitoring system of the instantinvention;

FIG. 7 is a plan view of another embodiment of a low pressure monitoringsystem of the instant invention;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Over Pressure Monitoring:

The vessel (12) is to be monitored for an over pressure situation.Current practice would be to simply place a high pressure switchdirectly on a sensing port (14) of the vessel (12). This provides noinformation to the operator on whether the high pressure switch isactually operable, or if the sensing port (14) is clogged. The instantinvention instead attaches a system chamber (10) to the sensing port(14) of the vessel (12) to be monitored, as shown in FIG. 1. A valve(16) operated by a solenoid (18) is placed in line between the systemchamber (10) and the sensing port (14). A high pressure switch (20) isconnected to the system chamber (10). The solenoid (18) is connected tothe high pressure switch (20), such that the valve (16) is caused toopen when the pressure in the system chamber (10) is higher than the setpoint of the high pressure switch (20). The system chamber (10) is alsoconnected to a gas source (24) which constantly supplies gas to thesystem chamber (10) through a constant flow regulator (26). The gassource (24) is maintained at a pressure that is greater than the setpoint of the high pressure switch (20).

In use, when the pressure in the system chamber (10) is lower than theset point of the high pressure switch (20), the solenoid (18) places thevalve (16) in the closed position. Gas continues to enter the systemchamber (10) through the constant flow regulator (26) from the gassource (24), causing the pressure in the system chamber (10) to rise.When the pressure in the system chamber (10) reaches the set point ofthe high pressure switch (20), the switch is triggered, which in turncauses the solenoid (18) to activate, opening the valve (16). The gas inthe system chamber (10) then escapes into the monitored vessel (12)though the valve (16) and sensing port (14), assuming that the pressurein the vessel (12) is lower than the pressure in the system chamber(10). As the gas escapes the system chamber (10) the pressure in thesystem chamber (10) is reduced until it falls below the set point of thehigh pressure switch (20). The high pressure switch (20) then resets,causing the solenoid (18) to close the valve (16), and the cycle beginsagain.

The cycling of the high pressure switch (20) also triggers a relay (28)which is connected to a sensing device (30). The sensing device (30)monitors the cycle of the high pressure switch (20). This may beaccomplished by monitoring the changing current demands placed upon thepower source (32) or by monitoring the contacts of the high pressureswitch (20). Any change in the cycle signals either an over pressureevent in the vessel (12), or a problem with the monitoring system. If,for example, there is an over pressure situation in the vessel (12),then, when the valve (16) opens, the pressure in the system chamber (10)will not fall below the set point of the high pressure switch (20). Thecycling will stop, and the sensing device (30) will alert the operator,or automatically take appropriate action. The sensing device (30) may bea computer programmed to recognize irregularities in the cycle. Thecycle can also be interrupted due to problems with the monitoringsystem. For example, if the sensing port (14) is clogged, then the gasin the system chamber (10) will not be able to escape into the vessel(12), meaning that the pressure will not fall below the set point of thehigh pressure switch (20), disrupting the cycle. Any failure in the flowof gas from the gas source (24) through the constant flow regulator (26)will also interrupt the cycle. A failure of the high pressure switch(20) will also interrupt the cycle.

The likelihood of clogging of the sensing port (14) is reduced by therelease of gas through the valve (16) and sensing port (14) with everycycle of the monitoring system. It is envisioned that Nitrogen, beinginert, would most often be the preferred gas. However, any gascompatible with the process occurring in the vessel (12) could be used.

The system continuously checks for an over pressure situation on themonitored vessel (12) as well as the failure of any component of themonitoring system. The frequency of the cycle can be adjusted by placinga restriction orifice a the mouth of the sensing port (14) or at theinlet or outlet of the valve (16). In this manner the time required forthe monitored vessel (12) to lower the pressure in the system chamber(10) can be increased.

In another embodiment of the system monitoring for an over pressuresituation, as shown in FIG. 2, the high pressure switch (20) isconnected directly to a three way valve (17) controlled by solenoid(19). The high pressure switch (20) is connected directly to the commonport of the three way valve (17) and will be connected to the gas source(24) when the solenoid valve is energized. The solenoid valve will beenergized when the high pressure switch (20) senses a pressure below itsset point. When the solenoid is energized, connecting the gas source(24) to the high pressure switch (20), the gas will cause the set pointof the high pressure switch (20) to be exceeded, causing the highpressure switch (20) to open, de-energizing the solenoid (19).De-energized, the solenoid (19) causes the three way valve (17) to blockin the gas source (24) and connect the high pressure switch (20) to themonitored vessel (12). The gas will escape into the monitored vessel(assuming the vessel is not in an over pressure state), until thepressure is reduced below the set point of the high pressure switch(20). When the pressure is reduced below the set point, the highpressure switch (20) closes, causing the solenoid (19) to energize,which starts the cycle over again. The cycle will continue until one ofthe components fails, or the pressure in the monitored vessel is abovethe set point of the high pressure switch (20). The needle valve (29)between the common port of the three way valve (17) and the highpressure switch (20) can be adjusted to extend or shorten the timerequired for the pressurized gas to escape into the monitored vessel,thereby extending or shortening the cycling frequency. The sensingdevice (30) may monitor the cycling by detecting the changing current inthe power source (32), or by monitoring the contacts of the highpressure switch (20).

In another embodiment of the system monitoring for an over pressuresituation, as shown in FIG. 3, the system chamber (10) is connected to asensing port (14) of the vessel (12) to be monitored. However, in thisembodiment the connection between the system chamber (10) and sensingport (14) includes a back pressure regulator valve (40). As gas is fedinto the system chamber (10) from the gas source (24) through theconstant flow regulator (26), the pressure in the system chamber (10)rises until the set point of the back pressure regulator (40) isreached, whereupon the back pressure regulator valve (40) opens,allowing gas to escape into the sensing port (14) and vessel (12). Asbefore, this tends to prevent the sensing port (14) from clogging withprocess material. Once the pressure in the system chamber (10) dropsbelow the set point of the back pressure regulator valve (40), the valvecloses, and the pressure begins to rise again, as gas fills the systemchamber (10), and the cycle begins anew. In this embodiment the cycle issensed by a pressure transmitter (42) which monitors the pressure in thesystem chamber (10). The pressure transmitter sends a signal to thesensing device (30) which determines if the cycle continues. If thecycling stops, the sensing device (30) will alert the operator, orautomatically take appropriate action. If the vessel (12) is overpressured, the back pressure regulator valve (40) will open, raising thepressure in the system chamber (10) upsetting the cycle. Also, anyfailure of the back pressure regulator valve (40), the pressuretransmitter (42), the constant flow regulator (26), and/or the gassource (24), will cause the cycle to be altered, which will be noted bythe sensing device (30).

A pressure transmitter (42) could also be used with the first embodiment(FIG. 1) to record the pressure at which the high pressure switch (20)was triggered. A change in the high pressure set point would indicate aproblem with either the high pressure switch (20), or the pressuretransmitter (42). The pressure transmitter signal (42) could also beused to activate the solenoid (18), replacing the high pressure switch(20) in that function.

The frequency of the cycle will also be impacted by the pressure in thevessel (12). The higher the pressure in the vessel (12) the longer itwill take for the gas to flow from the system chamber (10) into thevessel (12). The length of the cycle could be compared to the pressurein the vessel (12) as an additional check on the proper operation of thesystem. Changes in the cycle frequency that do not correlate to changesin the pressure in the vessel (12) can be used as indicators that somedegradation of the system is underway and preventative maintenance maybe needed.

In yet another embodiment of the system monitoring for an over pressuresituation, as shown in FIG. 4, a microprocessor (44) is connected to apressure transmitter (42) that is connected to the system chamber (10).The microprocessor (44) is programed to open and close the valve (16)through use of the solenoid (18) at certain pressures sensed by thepressure transmitter (42). A high pressure switch (20) is also attachedto the system chamber (10) and is connected to the sensing device (30).Monitoring of the cycles of the pressure switch (20) and/or the pressurecycles as sensed by the pressure transmitter (42) and recognition of anychanges in this cycle (particularly changes that do not correspond tochanges in the pressure in the vessel (12)) can be used to inform theoperator of an over pressure situation or of a failure or degradation ofthe monitoring system.

In yet another embodiment of the system monitoring for an over pressuresituation, as shown in FIG. 5, the means to raise the pressure in thesystem chamber (10) is a diaphragm or piston (46) that moves to reducethe volume of the system chamber (10), thereby raising the pressure inthe system chamber (10) to a point above the set point of the highpressure switch (20). The solenoid (18) is made to open and close valve(16) in concert with the movement of the diaphragm or piston (46), or inrelation to the status of the high pressure switch. When the highpressure switch (20) set point is exceeded the valve (16) is caused toopen. A spring (48) may be used to assist the motion of the diaphragm orpiston (46).

Certain industrial processes may require immediate shutdown in overpressure or under pressure situations due to safety concerns. However,system shutdowns can be expensive. Use of multiple monitoring devices ofthe type described herein will essentially eliminate false shutdowns,while insuring that a dangerous over or under pressure situation isdealt with appropriately. Where two or more monitoring systems are inplace on a pressure vessel, and only one of these systems experiences achange in the normal system cycle, it will be evident that the problemis with the monitoring system, not a vessel pressure that requiresshutdown. Only if the cycles of both monitoring systems change willshutdown be required.

Low Pressure Monitoring:

Some industrial processes require shutdown systems in case of underpressure situations to prevent the collapse of a vessel. The device tomonitor for under pressure situations is shown in FIG. 6, and comprisesa system chamber (10), connected to a sensing port (14) of the vessel(12) to be monitored. The system chamber (10) is also connected to a gassource (24) using a valve (17) controlled by solenoid (19). A lowpressure switch (21) is connected to eductor tube (50) which isconnected to the system chamber (10).

In use, the valve (17) opens, causing gas to flow toward the monitoredvessel (12), which is at a lower pressure than the gas source (24). Asthe gas flows past the eductor tube (50), the pressure sensed by the lowpressure valve (21) is reduced until the set point is reached. Thiscauses the solenoid (19) to cause the valve (17) to close, stopping theflow of gas into the system chamber (10). The pressure sensed by the lowpressure switch (21) then rises above the set point of the low pressureswitch (21), and the cycle begins again.

As with the high pressure systems described above, the cycle of the lowpressure switch (21) is monitored by a sensing device (30). Any changein the cycle is evidence of either a problem with the monitoring system,or a vessel under pressure situation.

An alternative embodiment of the low pressure monitoring system is shownin FIG. 7. As with the high pressure monitoring system shown in FIG. 5,the gas source (24) has been replaced with a diaphragm or piston (46)that moves to increase the volume of the system chamber (10) in concertwith the closing of valve (16), thereby lowering the pressure in thesystem chamber (10) below the set point of the low pressure switch (20).When the low pressure switch (20) reaches its set point, the diaphragmor piston (46) is caused to return to its original position, at the sametime as the valve (16) opens to connect the system chamber (10) with thevessel being monitored (12). A spring (48) may be used to assist themovement of the diaphragm or piston. Any change in the cycle, asmonitored by the sensing device (30), signals either a problem with themonitoring device, or a low pressure situation in the vessel (12).

It is intended that the foregoing detailed description be regarded asillustrative rather than limiting and that it is understood that thefollowing claims including all equivalents are intended to define thescope of the invention.

What I claim is:
 1. A cycling, self checking parameter monitoring systemcomprising;a parameter sensing switch with parameter value set point,said parameter sensing switch being connected to a system to bemonitored, whereby the parameter in the system is sensed by saidparameter sensing switch, means to alter the value of the parameterapplied to said parameter sensing switch without significantly alteringthe value of the parameter in the system to be monitored, whereby saidparameter value set point is reached, said means to alter beingtriggered by said parameter sensing switch not having reached saidparameter value set point, means to terminate the application of saidmeans to alter, said means to terminate being triggered by saidparameter sensing switch having reached said parameter value set point,whereby said parameter sensing switch returns to sensing the parameterin the system to be monitored, which in turn again triggers said meansto alter the value of the parameter, provided the value of the parameterin the system to be monitored has not reached said set point, and meansto recognize and monitor irregularities in the cycle created by theoperation of said means to alter the value of the parameter and saidmeans to terminate.
 2. A cycling, self checking parameter monitoringsystem as in claim 1 further comprising means to isolate said parametersensing switch from the system to be monitored when said means to alteris triggered.
 3. A process for monitoring a system parameter, comprisingthe steps of;connecting a parameter sensing switch with parameter valueset point to a system to be monitored, whereby the parameter in thesystem is sensed by said parameter sensing switch, altering the value ofthe parameter applied to said parameter sensing switch withoutsignificantly altering the value of the parameter in the system to bemonitored, said altering of the value to occur whenever said parametersensing switch has not reached said parameter value set point, wherebysaid parameter value set point is reached, terminating the altering ofthe value of the parameter applied to said parameter sensing switchwhenever said parameter value set point is reached, whereby saidparameter sensing switch returns to sensing the parameter in the systemto be monitored, which in turn again triggers the altering of the valueof the parameter applied to said parameter sensing switch, provided thevalue of the parameter in the system to be monitored has not reachedsaid parameter value set point, and recognizing and monitoringirregularities in the cycle created by altering and terminating thevalue of the parameter applied to said parameter sensing switch.
 4. Aprocess for monitoring a system parameter as in claim 3 furthercomprising the step of isolating said parameter sensing switch from thesystem to be monitored when altering the value of the parameter appliedto said parameter sensing switch.
 5. A vessel pressure monitoring systemcomprising;a three way valve with a common port, said three way valveattached to a vessel to be monitored for excess pressure at one of thenon-common ports of said three way valve, a high pressure switch with ahigh pressure set point, attached to the common port of said three wayvalve, a gas source attached to said three way valve at one of thenon-common ports, containing gas at a pressure higher than said setpoint of said high pressure switch, means for opening and closing saidthree way valve that depends upon the pressure sensed by said highpressure switch, whereby said common port of said three way valve isconnected to said gas source when the pressure sensed by said highpressure switch is less than said set point of said high pressureswitch, and whereby said common port of said three way valve isconnected to said vessel to be monitored when the pressure sensed bysaid high pressure switch is greater than said set point of said highpressure switch, and means to recognize and monitor irregularities inthe cycles of said high pressure switch.